It is known to provide magnetic chucks or workholding fixtures especially for flexible manufacturing operations. Magnetic chucks have been available for holding some magnetic workpieces. Suitably placed and oriented electrical coils permit the chuck to be magnetized to different levels and demagnetized for locating, securing and removing a magnetizable work piece as is described in the specifications and drawing figures of these patents. However, these chucks have not proven useful for securing and machining non-magnetic workpieces such as, e.g., cast aluminum alloys.
It is also known to provide a workholding fixture for securing and machining non-magnetic workpieces. An example of such a workholding fixture is disclosed in U.S. Pat. No. 6,644,637. In this patent, a workholding fixture includes an electromagnetic chuck and several modular fixture elements for locating, clamping, and supporting non-magnetic workpieces. Such a fixture is also useful for iron or steel workpieces. A magnetic chuck is one that can be energized and de-energized with an electric pulse from a stationary electric power source. Thus, the magnetic chuck provides a fast attach/release capability and a flat surface on which modular workpiece supporting, locating and clamping elements can be securely held by the magnetic force. Preferably, the strength of the magnetic field can be varied from a first level for sensitive and accurate modular element placement to a second, higher level for strongly securing the elements. In addition, the energized magnetic chuck can maintain its magnetic attractive force even when the chuck is disconnected from the power source.
In the above-described workholding fixture, the magnetic chuck should maintain its highest magnetic strength indefinitely when fully energized. However, unexpected loss of magnetic force can still happen due to imperfect surface conditions (e.g., nicks, scratches, chips) between the magnetic chuck and a base plate of the modular fixture elements as well as any possible deterioration of the magnetization circuitry.
One attempt has been made to measure the magnetic field to determine if it has sufficient strength. This attempt required an operator to use a Gauss meter to measure the magnetic field of the chuck through an opening at the bottom thereof. However, this process was labor intensive and costly.
Therefore, it is desirable to provide a magnetic force sensor for a workholding fixture that can measure an amount of magnetic force or magnetic field. It is also desirable to provide a magnetic force sensor to measure magnetic force or magnetic field in a magnetic workholding fixture. It is further desirable to provide a magnetic force sensor that can measure indirectly if magnetic force or magnetic field is sufficient in the magnetic workholding fixture. Thus, there is a need in the art to provide a magnetic force sensor assembly for a workholding fixture that meets these desires.